Amorebieta - Muxika

The BI-635 road between Amorebieta and Muxika is a safer road thanks to the works organised by the Bizkaia Provincial Council.

Image 1 of Amorebieta - Muxika

This is an initiative that improves accessibility in the area and reduces traffic and emissions in the centre of its urban areas.

Con una longitud de 3,4 kilómetros, el corredor ejecutado comienza en la glorieta de conexión con la AP-8 y la N-634. El tramo a cielo abierto se apoya puntualmente sobre el trazado antiguo de la carretera BI-635 mientras que el Alto de Autzagane se salva gracias al túnel de Urdinbide.

The new Urdinbide tunnel offers a safer and more comfortable alternative to passing through the Alto de Autzagane.

Its construction has posed both a technical hurdle and a major environmental challenge in terms of preserving the existing aquifer. To achieve this, innovative technical solutions have been designed, such as pre-injections to improve and waterproof the ground, which have made it possible the excavation of the tunnel to be carried out in compliance with all safety and environmental requirements.

This new infrastructure adds to Bizkaia's provincial road network, offering a modern, safer, cleaner, and more sustainable route. In short, this is an initiative that contributes to improving the quality of life of the region's residents and increases the competitiveness of its companies thanks to a safer, faster, and more efficient connection.

Cut and cover

Key figures

  • 570,000 m3 of excavation
  • 490,000 m3 of embankment backfilling
  • 11,000 m3 of concrete
  • 1,500,000 kg of steel
  • 4 underpasses
  • 8 concrete walls
  • 5 breakwater walls
  • 2 reinforced soil walls
  • 5 pile walls
  • 2 micropile walls
  • 17 transverse drainage works
  • 42,000 m3 of soil cement
  • 40,000 tn of hot asphalt mixes
  • 4,827 m2 of anti-noise screens

Initial distributor roundabout (Betarragane)

The initial roundabout located in the Betarragane neighbourhood, with two 3.50 m wide lanes and an external diameter of 56 m, constitutes the beginning of the project. It is located next to the AP-8 and receives all traffic in and out of the N-634 as well as an exit branch of the AP-8. It also includes a new branch to join the N-634 (towards Bilbao) from the BI-635 which, alongside the support of the roundabout at C/ San Juan, allows access to the N-634 towards Donostia.

Calle Karmen roundabout

This new roundabout, with two 3.50 m wide lanes and an outer diameter of 45.30 metres, together with the Betarragane roundabout, facilitates traffic calming before connecting with the roads to which it provides access: BI-635, AP-8, and N-634. It also makes it possible to pedestrianise the urban centre of Amorebieta, given that before these works were carried out, it was necessary to go through the BI-635 to reach the AP8 and the N-634.

Poitoa semi-junction

The Poitoa junction, located on the road in the direction of Amorebieta, allows both inbound and outbound traffic and ultimately serves the existing properties on the left bank of the corridor. This junction is formed of two axes, one at the entrance and the other at the exit to the main trunk, which facilitate the aforementioned routes. The Poitoa semi-junction has a section that is shared simultaneously by pedestrians and bicycles, connecting the area's neighbourhoods.

Katia junction

Designed as a "diamond interchange" type junction, it facilitates all possible routes within the BI-635. The junction formed by four connecting branches between said junction and the trunk road, and by the two roundabouts with an outer diameter of 26 m and 28 m respectively, which regulate traffic.

Tunnel section. Alto Autzagane Bypass

Key figures

  • 2-tube tunnel 695 metres long
  • Lanes per tube: 2
  • Width of the lanes: 3.50 metres
  • Width of the right-hand verge: 2.50 metres
  • Width of the left-hand verge: 1.00 metre
  • Width of the pavement: 0.75 metres
  • Standard minimum clearance: 5 metres
  • Cladding: 40 cm thick HM30 mass concrete with anti-spalling fibres
  • Interconnecting galleries between tubes: 2 (for pedestrians)


The Urdinbide tunnel itself constitutes the bypass section of the new BI-635 on the Alto de Autzagane road. The part corresponding to the excavated tunnel has a length of some 538 metres and the cut and cover tunnels that made it possible to carry out the excavation have a length of 112 metres at the south opening and 45 metres at the north opening.

With regard to Urdinbide Tunnel, all the tunnel's control, surveillance, and security systems are connected by fibre optics to the Control Centre (MKZ), located at the entrance to the Malmasin tunnels, from where the tunnel is operated. The centralised control system allows operators to fully monitor and manage all the installations in the tunnels through the signals and alarms that are present in the infrastructure and through the automation systems implemented for the more complex systems (e.g. ventilation and lighting).


The works carried out include improvements, with the importance and impact on the surroundings of the works being described below:

  • There is a cycle lane and a service road separated from the main road by acoustic screens along the cut and cover stretch between calle Karmen and the Katia neighbourhood in the direction of Alto de Autzagane, in order to promote sustainable urban mobility and reduce greenhouse gas emissions produced by other means of motorised transport
  • A new access to the N-634 towards Donostia that prevents traffic between Busturia and Durango from having to cross the town of Amorebieta.
  • Re-surfacing, renewal of the wearing course, and adaptation of the containment systems on the BI-635 in the area around Gorozika

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